The present invention relates to a method of preparing crystalline sugar which provides unique structure and controlled crystal size, and the product resulting therefrom.
Crystallization is one of the oldest industrial chemical transformation processes known. Vast quantities of crystalline substances are produced for commercial purposes, e.g., in excess of 100.times.10.sup.6 metric tons per year. One of the most common products prepared by crystallization is sugar.
Crystallization of sugar is complex. The growth of crystals involves simultaneous transfer of heat and mass in a multi-phase, multi-component system. While the coexistence of these conditions alone present complex control problems, fluid and particle mechanics and thermodynamic instability create further complications.
Conventional wisdom in the science of sugars teaches crystallization by supersaturation. Supersaturation requires removal of water. Cooling, evaporating, and precipitating are used. Manufacturing procedures for crystallizing sugar are heat and energy intensive. Moreover, nucleation of sugar crystals during supersaturation is relatively uncontrollable. Consequently, the size and shape of the resulting crystals are unpredictable.
The drawbacks of known sugar manufacturing procedures are especially manifested when preparing sugar having reduced-size crystals. Reduced-size crystalline sugar product is referred to herein as microcrystals. Individual particles of microcrystalline product are no greater than 50 .mu.m.
For example, one method of manufacturing reduced-size crystals involves grinding and sieving crystalline sugar. Grinding is energy intensive. Moreover, fracturing sugar results in a wide distribution of ground sugar crystals. The large crystals must be reground and sieved. Much of the product is lost as fines. Thus, grinding and sieving is expensive and inefficient.
U.S. Pat. No. 3,981,739 to Dmitrovsky, et al. discloses preparation of crystalline sugar from solution by 1) concentrating a solute in the presence of seed crystals added thereto, followed by 2) further removal of solvent through heating and evaporation of the stream resulting from the first stage concentration. This energy intensive procedure produces sugar crystals having an average size in the range of 325-425 microns. The Dmitrovsky, et al. '739 disclosure is a solution process which relies on nucleation by addition of seed crystals while concentrating by high heat and vacuum evaporation. The same procedure is disclosed in U.S. Pat. No. 4,056,364 to Dmitrovsky, et al.
U.S. Pat. No. 4,159,210 to Chen, et al. describes a method for preparing crystallized maple sugar product by 1) concentrating maple syrup to a solids content of about 93-98% in the presence of heat and partial vacuum, and 2) impact heating until transformation and crystallization of the syrup occur. The product may then be cooled, milled and screened to a suitable size range. The Chen, et al. '210 procedure is energy intensive, relies on "beating" to induce nucleation of the crystals, and calls for subsequent milling to obtain reduced-size crystals.
In U.S. Pat. No. 4,362,757 to Chen, et al. a crystallized sugar product and a method of preparing same are described. The method disclosed in the Chen, et al. '757 reference includes concentrating sugar syrups to a solids content of about 95% to about 98% by heating to a temperature of about 255.degree. F. to about 300.degree. F. The resulting concentrated syrup is maintained at a temperature not less than about 240.degree. F. in order to prevent premature crystallization. A premix consisting of an active ingredient (e.g., a volatile flavor, an enzyme, an acidic substance such as ascorbic acid, a fruit juice concentrate, or a high invert sugar substance) is mixed with the concentrated sugar syrup. The combination is subjected to impact heating until a crystallized sugar product made up of fondant-size sucrose crystals and the active ingredient is formed which has a moisture content of less than 2.5% by weight. The Chen, et al. '757 process requires heat intensive concentrating and heating for nucleation.
A similar procedure is disclosed in U.S. Pat. No. 4,338,350 to Chen, et al. wherein a process for preparing a crystallized sugar product containing a food ingredient is described. The Chen, et al. '350 disclosure calls for concentrating a sugar syrup at a temperature range of about 250.degree. F. to about 300.degree. F. to a solids content of about 90 to 98% by weight. A food ingredient, such as gelatin, cocoa powder, pectin concentrate, etc., is admixed with the sugar syrup. The mixture is subjected to impact beating until a crystallized sugar product made up of aggregates of fondant-size sucrose crystals and food ingredients is formed. The Chen, et al. '350 process requires heat intensive concentrating and beating to induce crystallization.
U.S. Pat. No. 3,365,331 to Miller, U.S. Pat. No. 4,338,350 and U.S. Pat. No. 4,362,757 describe a process for crystallizing sugar, which involves impact beating a sugar solution to provide nucleation. The process involves input of considerable amount of energy and has problems directly related to temperature control.
Other disclosures include British Patent Specification No. 1 460 614 and U.S. Pat. No. 3,972,725 (Tate & Lyle Limited) which disclose a continuous process wherein a syrup solution is catastrophically nucleated and discharged into a crystallization zone. Catastrophic nucleation is achieved by subjecting the solution to shear force which can be applied in apparatus such as a colloid mill or homogenizer. The solution is discharged onto a moving band where the water must be boiled off by maintaining the material at a relatively high temperature. A related process has been disclosed in British Patent Specification 2 070 015 B and U.S. Pat. No. 4,342,603, which is used for crystallization of glucose. In the disclosed procedure, a supersaturated solution is subjected to shear force and allowed to crystallize on a belt. Both the sucrose process and the glucose process require solution processing at high temperatures and are, consequently, energy intensive.
U.S. Pat. No. 3,197,338 to Hurst, et al. discloses a process for crystallizing glucose which includes kneading a glucose solution to induce nucleation followed by crystallization to form a solid glass which is then ground. Another glucose crystallization process has been disclosed in GB 2 077 270 B in which starch hydrolyzate is concentrated by evaporation and then simultaneously crushed and mixed during crystallization while cooling. The product is further milled. These processes also require nucleating by beating a solution which includes glucose.
UK Patent Specification G B 2 155 934 B of Shukla, et al. discloses a method for crystallizing sucrose or glucose from a solution. Shukla, et al. subject a sugar solution to evaporation to produce a supersaturated sugar solution. The supersaturated solution is then subjected to shear in a continuous screw extruder to induce nucleation. The retention time of the syrup is below 25 seconds (on the average) at a temperature of 115.degree. C. to 145.degree. C. (239.degree. F.-293.degree. F.) for sucrose and 100.degree. C.-135.degree. C. (215.degree. F.-275.degree. F.) for glucose. After the syrup is subjected to progressive nucleation, Shukla, et al. pass the syrup onto a moving band to permit crystallization to continue at a gradual rate at relatively high temperature. The Shukla, et al. process requires maintenance of the solution at temperatures which do not drop below the boiling point of water.
Additional technology has been developed which relates to processing food and food ingredients. For example, a series of U.S. patents issued to Thomas E. Chivers (U.S. Pat. No. 3,762,846, U.S. Pat. No. 3,723,134, and U.S. Pat. No. 3,557,717) disclose a solution process for making candy floss from a cooked slurry or syrup. The ingredients are blended and heated at a first temperature, e.g., 200.degree.-205.degree. F. (93.degree.-96.degree. C.), to form a slurry. After forming the slurry, the batch is cooked or boiled at a substantially higher temperature, e.g., about 340.degree. F. (171.1.degree. C.), and thereafter discharged through an atomizing nozzle. Most of the moisture contained in the molten candy flashes off as it is discharged. The Chivers disclosures rely on dissolution of the ingredients, e.g., sugar and other ingredients, in water and then heating extensively to drive the water from the solution. Most of the water is driven off after discharging the solution. Thus, the Chivers technology suffers from drawbacks associated with sustained high temperature processing and dissolution of ingredients during processing.
Another method for process material is disclosed in European Patent Application 0 387 950 A1 of Stork. The Stork process is a method of preparing a foam spray-dried product by collision of a stream of gas which contains dry particulate material, with a jet of droplets of a liquid solution. A liquid solution which contains at least one of the ingredients of the end product is combined with gas and heated before spraying as a jet of droplets for collision with the dry particulate. The Stork system is designed to process a low density product; it requires an elaborate equipment arrangement, and is energy intensive.
In U.S. Pat. No. 3,615,671 to Shoaf discloses a method of producing food products by encasing dry particulate food particles within a casing of spun sugar filaments. In order to enhance 1) shaping of the fibers and particles and 2) the tendency of the fibers to stick to each other with a minimum of compression, Shoaf uses a humectant in the sugar mix to be spun and controls the relative humidity of the gases surrounding the filaments as they are spun. The humectants described as useful are as follows: invert syrup or corn syrups and polyhydric alcohols, e.g., sorbitol, glycerol and pentahydric alcohols, e.g., xylitol. Shoaf is concerned with preventing crystallization of the spun sugar in order to enable the manufacturer to encase dry food particles by wrapping and compressing filaments of the spun sugar around the particles.
More recently, a trade brochure provided by Domino Sugar Corporation, Industrial Products, entitled "Co-Crystallization" (undated) describes a product in which microsized crystals form aggregates having a second ingredient disposed over the surface of each aggregate. The process for producing this new product requires that all starting materials must be in a liquid state. Therefore, solvent must be driven off by heat and/or vacuum in order to concentrate the syrup from crystalline growth. As in other solution process energy is required to transform the sugar to microsized crystals.
Inherent in the procedures set forth above, as well as other procedures known in the art, is the technical philosophy of dehydration to promote crystallization. Supersaturation, pan drying, and nucleation by agitation or chemical reaction depend on the principle of eliminating water to form crystals. A common difficulty with crystallization based on this technical underpinning has been lack of control over crystalline growth.
Thus, it would be significant advance in the art of crystallization, to provide a mechanism for crystal formation which departs from traditional dehydration, and which provide a low energy means for producing a crystalline sugar product.
Accordingly, it is an object of the present invention to enable the artisan to make a sugar product which has a predictable crystalline growth and uniform crystal size without energy-intensive procedures. Other objects and surprising new sugar-crystal technology are disclosed in the remainder of the Specification.